1. Title of the Invention
The present invention relates to a developing unit for conducting development on a latent image carrier on which an image is formed, and also relates to an image forming apparatus, having the developing unit, to form an image and to transfer the formed image onto a recording medium.
2. Description of the Related Art
In a conventional image forming apparatus, a latent image is formed on a latent image carrier, and development is conducted on the latent image carrier by a developing unit, and then the developed image is transferred onto a sheet of paper which is a recording medium. In the above developing process, toner is used.
There is provided a developing method in which development is conducted as follows. In the developing process in which a latent image formed on the latent image carrier is developed with toner, a carrier to convey toner is used so that the development can be effectively conducted.
According to the above developing method, the carrier is circulated in the developing unit to develop the latent image, so that toner can be fed to the latent image carrier.
However, in a printing apparatus in which toner is used for printing, toner is transferred onto a sheet of paper which is a recording medium. Therefore, the quantity of toner accommodated in the printing apparatus is reduced each time it is used. Accordingly, it is necessary to feed toner to the developing unit.
The carrier is deteriorated by the friction when it is circulated in the developing unit, and it becomes impossible for the carrier to convey toner. For this reason, it is necessary to replace the carrier after it has been used over a predetermined period of time.
In the above type of image forming apparatus, a multicolor printer including a plurality of developing units and latent image carriers has come into wide use.
However, in the above image forming apparatus, a developer which contains toner and a carrier is manually replaced by an operator, so that it takes much time and labor. Moreover, in the apparatus of multicolor printing, it is necessary to replace developer for each color. Therefore, it takes more time to replace developer of each color.
Accordingly, it is preferable to save time and labor in the process of replacing developer. Further, it is preferable to extend the life of the developer.